Melanoma is one of the most lethal forms of cancers. The major reason for lack of satisfactory management of melanomas is our poor understanding of the biology of melanoma pathogenesis. Recently, regulation of mRNA fate in the cytoplasm emerged as a major mechanism controlling gene expression. RNA-binding proteins afford another dimension of the regulation of pathways involved in tumor progression. IGF2BP1 is an RNA-binding protein that regulates stability, localization and translation of its mRNA targets. We have previously shown that RNA-binding protein IGF2BP1 is overexpressed in melanomas, however the role of IGF2BP1 in pathogenesis of melanoma has not been elucidated. Our new preliminary data in different mouse models show that IGF2BP1 affects melanoma metastasis and its high expression in human melanoma correlates with poor clinical outcomes. Based on our previous studies and new exciting observations we hypothesize that IGF2BP1 plays a key role in melanoma progression and metastasis. To test this hypothesis, we propose the following independent, but highly interrelated specific aims: Specific Aim 1. To analyze mechanisms of IGF2BP1 function in melanoma metastasis. This aim is designed to identify IGF2BP1 targets responsible for the function of IGF2BP1 in melanoma metastasis. To this end we propose several complementary approaches to perform an unbiased analysis of IGF2BP1 involvement in melanoma metastasis. Our approach will include: i) analysis or RNA downregulated upon inhibition of IGF2BP1 function in melanoma in vivo; ii) in vivo analysis of cDNAs capable of overcoming the inhibition of melanoma metastases caused by IGF2BP1 down-regulation; iii) analysis of changes in half-life and expression of mRNA upon IGF2BP1 inhibition in melanoma; and iv) identification of mRNAs directly interacting with IGF2BP1 in metastatic melanoma cells. Specific Aim 2. To analyze the role of IGF2BP1 in EV-mediated melanoma progression. This aim is designed to comprehensively evaluate the function of IGF2BP1 in melanoma EV, especially as it relates to their role in tumor progression. Our analysis will include the elucidation of the IGF2BP1 in EV-mediated pre-metastatic niche formation; its role in EV uptake by recipient cells in vitro and in vivo; efficiency of RNA transfer to recipient cells; analysis of EV number, size, composition and cargo; and validation of our findings in EV isolated from the serum of melanoma patients. Impact: On successful completion of this study, we will: (a) understand the contribution and mechanisms of IGF2BP1 involvement in melanoma progression; (b) better understand how IGF2BP1 and its target genes are involved in melanoma metastasis; and (c) establish IGF2BP1 as a novel therapeutic target for melanoma patients. The proposed studies which combine cellular and molecular biology, bioinformatics, technology development, and cutting-edge in vivo experimentation will provide insights into the interplay between the IGF2BP1 and its target molecules and how these contribute to melanoma progression. Ultimately, the data obtained in this study have a potential to pave the way for new therapeutics in melanoma.